Effects of heavy metals on the biology of a N2‐fixing cyanobacterium Anabaena doliolum

The effects of copper, nickel, and iron on survival, growth, nutrient uptake (NH, NO, and PO), carbon fixation, nitrate reductase, nitrogenase (CH2 reduction assay), glutamine synthetase (transferase), and alkaline phophatase activities of Anabaena doliolum were studied. About 50% survival of the test alga was scored at 8.0 × 10−3, 8.6 × 10−3, and 0.36 mM of Cu, Ni, and Fe, respectively. However 45, 59, and 57% reductions in final yield were scored, respectively, at LD50 concentrations of Cu, Ni, and Fe. On the basis of the LD50 of the test metals, Ni was the most inhibitory for nutrient uptake. However, the LD50 concentrations of Cu, Ni, and Fe showed different levels of inhibition for different processes. Although metal concentrations higher than LD50 were found to be more inhibitory, 0.54 mM iron generated maximum inhibitory effect as compared to Cu and Ni. The present study demonstrates that the test cyanobacterium exhibits metal and dose-specific responses toward different physiological and biochemical processes.